Drug delivery device and logging module assembly

ABSTRACT

A drug delivery assembly comprises a drug delivery device, an electronic dose logging module releasably attachable to the drug delivery device, and a cap releasably attachable to the logging module to cover an outlet portion of a mounted drug reservoir. The logging module and the drug delivery device comprise mating snap coupling means. The logging module comprises locking means acting on the locking module snap coupling means, wherein the locking means is actuated from the unlocked to the locked state when the cap is attached to the logging module in a first direction, and the locking means is actuated from the locked to the unlocked state when the cap is detached from the logging module in a second direction opposed to the first direction.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a 35 U.S.C. §371 National Stage application ofInternational Application PCT/EP2014/056725 (published asWO2014/161953), filed Apr. 3, 2014, which claims priority to EuropeanPatent Application 13162516.2, filed Apr. 5, 2013; this applicationclaims priority under 35 U.S.C. §119 to U.S. Provisional Application61/810,051; filed Apr. 9, 2013.

The present invention generally relates to medical devices for which thegeneration, collecting and storing of data are relevant. In specificembodiments the invention relates to systems and devices for capturingdrug delivery dose data in an efficient and user-friendly way.

BACKGROUND OF THE INVENTION

In the disclosure of the present invention reference is mostly made todrug delivery devices comprising a threaded piston rod, such devicesbeing used e.g. in the treatment of diabetes by delivery of insulin,however, this is only an exemplary use of the present invention.

Drug Injection devices have greatly improved the lives of patients whomust self-administer drugs and biological agents. Drug Injection devicesmay take many forms, including simple disposable devices that are littlemore than an ampoule with an injection means or they may be durabledevices adapted to be used with pre-filled cartridges. Regardless oftheir form and type, they have proven to be great aids in assistingpatients to self-administer injectable drugs and biological agents. Theyalso greatly assist care givers in administering injectable medicines tothose incapable of performing self-injections.

Performing the necessary insulin injection at the right time and in theright size is essential for managing diabetes, i.e. compliance with thespecified insulin regimen is important. In order to make it possible formedical personnel to determine the effectiveness of a prescribed dosagepattern, diabetes patients are encouraged to keep a log of the size andtime of each injection. However, such logs are normally kept inhandwritten notebooks, from the logged information may not be easilyuploaded to a computer for data processing. Furthermore, as only events,which are noted by the patient, are logged, the note book systemrequires that the patient remembers to log each injection, if the loggedinformation is to have any value in the treatment of the patient'sdisease. A missing or erroneous record in the log results in amisleading picture of the injection history and thus a misleading basisfor the medical personnel's decision making with respect to futuremedication. Accordingly, it may be desirable to automate the logging ofejection information from medication delivery systems.

Though some injection devices integrate this monitoring/acquisitionmechanism into the device itself, e.g. as disclosed in US 2009/0318865and WO 2010/052275, most devices of today are without it. The mostwidely used devices are purely mechanical devices either durable orprefilled. The latter devices are to be discarded after being emptiedand so inexpensive that it is not cost-effective to build-in electronicdata acquisition functionality in the device it-self. Addressing thisproblem a number of solutions have been proposed which would help a userto generate, collect and distribute data indicative of the use of agiven medical device.

For example, WO 2007/107564 describes an electronic “add-on” moduleadapted to be attached to and measure signals generated by a mechanicalpen device. The detected signals may be used to detect different events,e.g. different sounds indicating setting a dose respectively ejecting adose. A memory stores detected doses together with a time stamp, e.g.for several months. The module is provided with wireless means fortransmitting detected data to an external unit, e.g. computer or anotherportable device (e.g. cell phone, PDA) for further processing andvisualization. WO 2010/037828 discloses an arrangement for mounting sucha module on a pen-formed drug delivery device. Further external devicesfor a pen device are shown in U.S. Pat. No. 6,482,185, and WO 03/005891.

Having regard to the above, it is an object of the present invention toprovide devices and methods allowing secure, easy and cost-effectiveoperation of a drug delivery assembly comprising a user-mountablemodule.

DISCLOSURE OF THE INVENTION

In the disclosure of the present invention, embodiments and aspects willbe described which will address one or more of the above objects orwhich will address objects apparent from the below disclosure as well asfrom the description of exemplary embodiments.

Thus, in a first aspect of the invention a drug delivery assembly isprovided, comprising a drug delivery device, a logging module and a cap.The drug delivery device comprises a drug reservoir or means forreceiving a drug reservoir, as well as drug expelling means. The loggingmodule is releasably attachable to the drug delivery device andcomprises electronic circuitry adapted to create a log of expelled doseamounts of drug, the logging module comprising sensor means adapted tocapture a property value related to a dose amount of drug expelled froma reservoir by the expelling means during an expelling event, andprocessor means adapted to determine dose amounts based on capturedproperty values. The cap is releasably attachable to the logging moduleto cover an outlet portion of a mounted drug reservoir. In such anassembly the logging module and the drug delivery device comprise matingsnap coupling means allowing the logging module and the drug deliverydevice to be releasably coupled to each other by relative movement therebetween in a first direction, and the logging module comprises lockingmeans acting on the locking module snap coupling means and beingactuatable between a locked and an unlocked state. The locking means isactuated from the unlocked to the locked state when the cap, with thelogging module coupled to the drug delivery device, is attached to thelogging module in the first direction, and the locking means is actuatedfrom the locked to the unlocked state when the cap is detached from thelogging module in a second direction opposed to the first direction.

By this arrangement the likelihood that the logging module is beingunintentionally pulled off the drug delivery device when the cap isremoved from the device can be reduced, the arrangement at the same timeensuring that it is easy to securely attach the module to the drugdelivery device and subsequently remove it again.

The locking means may in the locked state prevent the logging modulefrom being de-coupled from the drug delivery device (an “absolute” lock)or the locking means may in the locked state provide that an increasedforce has to be applied in order to de-couple the logging module fromthe drug delivery device.

The logging module snap coupling means may comprise a flexible portionbeing strained in the attached state, wherein the locking means in thelocked state increases the strain. The cap may attach solely to thelogging module or it may engage both the logging module and the drugdelivery device when attached.

When the logging module is not attached to the drug delivery device, thecap may be releasably attachable to the drug delivery device.

In an exemplary embodiment the drug delivery device comprises anexpelling assembly actuatable between a dose setting state and anexpelling state, the dose setting state allowing a user to set a givendose amount to be expelled, and the expelling state allows the expellingassembly to expel the set dose by moving the piston of a loadedcartridge distally. The expelling assembly may comprise a spring whichis strained during dose setting and which is released in the expellingmode to drive the expelling assembly.

In order to detect the dose amounts to be logged, the expelling assemblycomprises in an exemplary embodiment an indicator element having amagnet moving together therewith, and the logging module comprises asensor assembly with one or more sensors which in combination withprocessor means are adapted to capture property values. The magnet isconfigured to generate a spatial magnetic field which relative to thesensor assembly varies corresponding to the spatial position andorientation of the magnet and thus the indicator element, therebygenerating a spatial magnetic field which varies uniquely relative toeach sensor, wherein the indicator element is adapted to (i) rotateduring expelling operation of the assembly, and (ii) move axially duringactuation operation of the assembly between the dose setting and theexpelling state. The processor means is configured to determine on thebasis of measured values (i) an axial position of the indicator element,and (ii) a rotational position of the indicator element. The informationcaptured in this way can be used to determine an expelled dose in aneffective way. When the logging module is turned on, e.g. when the capis removed, a first absolute rotational position of the indicatorelement is determined, then it can be determined when the indicatorelement is moved axially to the expelling position and moved back to itsdosing position, this indicating that a dose has been expelled.Determining a second absolute rotational position of the indicatorelement then allows the expelled dose amount to be determined. Ifexpelling has just been halted the next actuation cycle will result in asecond dose amount to be determined.

Indeed, in case the indicator element can rotate more than one turn thenumber of turns will have to be determined, e.g. by detecting full turnsof the indicator element or by detecting axial movement of an elementbeing moved axially corresponding to cartridge piston. Examples of thelatter would be a piston rod or an end-of-content member.

Correspondingly, in an exemplary embodiment a system is providedcomprising a first sensor assembly comprising one or more sensors eachadapted to measure a magnetic field, a second sensor assembly comprisingone or more sensors each adapted to measure a magnetic field, and amechanical assembly comprising the indicator element. The processormeans is configured to determine (i) on the basis of measured valuesfrom the first sensor assembly a rotational position of the indicatorelement, and (ii) on the basis of measured values from the second sensorassembly the number of full rotations of the indicator element. Thefirst sensor assembly may have a first sampling frequency, and thesecond sensor assembly may have a second higher sampling frequency. Thelatter arrangement will allow a more energy efficient system as “simple”rotation typically can be measured using a single low-power sensorwhereas the precise determination of a given position typically requiresthe use of two or more high-power sensors.

In the above-described systems the indicator element may be formed atleast in part of a polymeric material containing magnetic particles, thepolymeric material having been magnetized to provide a magnet producingthe magnetic spatial field, e.g. the indicator element may be in theform of a ring-formed uniform member.

To prevent that a given logging module is used in a way resulting inincorrect determination of dose data, the system comprises in exemplaryembodiments means to ensure that a given logging module in a given stateis used in combination with the corresponding drug.

Correspondingly, the logging unit may be provided with an electronicallycontrolled means for capturing information from an identifier on thedrug delivery device, such that a log is created for a given identifier.The identifier may represent a given specific type of drug or a givenunique drug delivery device. The identifier may be in the form of acolour marking, a barcode (e.g. 2D) or in the form of a pattern ofconductive elements. The means for capturing information from theidentifier may comprise a sensor adapted to capture information duringmovement of the sensor relative to the identifier.

Designing an electronic logging unit, that can automatically identifyand recognise drug delivery devices with different contents will allowmanufacturers a simpler and more cost efficient production and provideincreased safety of the users.

In the context of the present application and as used in thespecification and the claims, the term processor means covers anycombination of electronic circuitry suitable for providing the specifiedfunctionality, e.g. processing and storing data as well as controllingall connected input and output devices. A processor will typicallycomprise one or more CPUs or micro-processors which may be supplementedby additional devices for support, storage or control functions. Forexample, in case a communication interface is provided (e.g. wireless),the transmitter and receiver may be fully or partly integrated with aprocessor, or may be provided by individual units. Each of thecomponents making up the processor circuitry may be special purpose orgeneral purpose devices. The term display means covers any type ofdisplay capable of visually providing the specified functionality, e.g.a LCD or OLED.

As used herein, the term “insulin” is meant to encompass anydrug-containing flowable medicine capable of being passed through adelivery means such as a cannula or hollow needle in a controlledmanner, such as a liquid, solution, gel or fine suspension, and whichhas a blood glucose controlling effect, e.g. human insulin and analoguesthereof as well as non-insulins such as GLP-1 and analogues thereof. Inthe description of exemplary embodiments reference will be made to theuse of insulin.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following the invention will be further described with referenceto the drawings, wherein

FIG. 1A shows a system comprising a logging module mounted on a pendevice,

FIG. 1B shows the system of FIG. 1A with the pen cap removed,

FIG. 2 shows in an exploded view the components of the pen device ofFIG. 1A,

FIGS. 3A and 3B show in sectional views an expelling mechanism in twostates,

FIGS. 4A-4C show components of the pen device of FIG. 2,

FIG. 5 shows a component of the pen device of FIG. 2,

FIG. 6 shows components of a first embodiment of a logging module,

FIG. 7 shows components of a second embodiment of a logging module,

FIG. 8 shows a component of a third embodiment of a logging modulemounted on a pen,

FIG. 9 shows a component of a fourth embodiment of a logging module, and

FIG. 10 shows an exterior view of the fourth embodiment of a loggingmodule.

In the figures like structures are mainly identified by like referencenumerals.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

When in the following terms such as “upper” and “lower”, “right” and“left”, “horizontal” and “vertical” or similar relative expressions areused, these only refer to the appended figures and not necessarily to anactual situation of use. The shown figures are schematic representationsfor which reason the configuration of the different structures as wellas their relative dimensions are intended to serve illustrative purposesonly. When the term member or element is used for a given component itgenerally indicates that in the described embodiment the component is aunitary component, however, the same member or element may alternativelycomprise a number of sub-components just as two or more of the describedcomponents could be provided as unitary components, e.g. manufactured asa single injection moulded part. When it is defined that members aremounted axially free to each other it generally indicates that they canbe moved relative to each other, typically between defined stoppositions whereas when it is defined that members are mountedrotationally free to each other it generally indicates that they can berotated relative to each other either freely or between defined stoppositions. The terms “assembly” and “subassembly” do not imply that thedescribed components necessary can be assembled to provide a unitary orfunctional assembly or subassembly during a given assembly procedure butis merely used to describe components grouped together as beingfunctionally more closely related.

FIGS. 1A and 1B show a drug delivery assembly 1 with a pen-formed drugdelivery device 200 on which an electronic logging module 100 ismounted. In the present context the device represents a “generic” drugdelivery device providing a specific example of a device in combinationwith which embodiments of the present invention is intended to be usedor which can form a basis for aspects of the present invention.

More specifically, the logging module 100 comprises a body portion 110and a ring-formed portion 120 allowing the module to be mounted on agenerally cylindrical pen device. The body portion comprises electroniccircuitry and sensor means allowing a property to be detectedrepresenting an amount of drug being expelled from the cartridge, aswell as a display 130 for displaying data to a user. The ring portioncomprises coupling means allowing the module to be securely andcorrectly mounted on the pen body. The electronic circuitry and thesensor means may in part be arranged in the ring portion. Exemplaryembodiments of a logging module will be described with reference toFIGS. 6-10 below.

The pen device 200 comprises a cap part 207 and a main part having aproximal body or drive assembly portion with a housing 201 in which adrug expelling mechanism is arranged or integrated, and a distalcartridge holder portion in which a drug-filled transparent cartridge213 with a distal needle-penetrable septum is arranged and retained inplace by a non-removable cartridge holder attached to the proximalportion, the cartridge holder having openings allowing a portion of thecartridge to be inspected as well as distal coupling means 215 allowinga needle assembly to be releasably mounted. The cartridge is providedwith a piston driven by a piston rod forming part of the expellingmechanism and may for example contain an insulin, GLP-1 or growthhormone formulation. A proximal-most rotatable dose member 280 serves tomanually set a desired dose of drug shown in display window 202 andwhich can then be expelled when the button 290 is actuated. Depending onthe type of expelling mechanism embodied in the drug delivery device,the expelling mechanism may comprise a spring as in the shown embodimentwhich is strained during dose setting and then released to drive thepiston rod when the release button is actuated. Alternatively theexpelling mechanism may be fully manual in which case the dose memberand the actuation button moves proximally during dose settingcorresponding to the set dose size, and then is moved distally by theuser to expel the set dose.

As appears, FIG. 1 shows a drug delivery device of the pre-filled type,i.e. it is supplied with a pre-mounted cartridge and is to be discardedwhen the cartridge has been emptied. In alternative embodiments the drugdelivery device may be designed to allow a loaded cartridge to bereplaced, e.g. in the form of a “rear-loaded” drug delivery device inwhich the cartridge holder is adapted to be removed from the device mainportion, or alternatively in the form of a “front-loaded” device inwhich a cartridge is inserted through a distal opening in the cartridgeholder which is non-removable attached to the main part of the device.

As the invention relates to a module adapted to be secured to andinteract with a drug delivery device, as well as a drug delivery deviceallowing such an interaction, an exemplary embodiment of such a devicewill be described for better understanding of the invention.

FIG. 2 shows an exploded view of the pen-formed drug delivery device 200shown in FIG. 1. More specifically, the pen comprises a tubular housing201 with a window opening 202 and onto which a cartridge holder 210 isfixedly mounted, a drug-filled cartridge 213 being arranged in thecartridge holder. The cartridge holder is provided with distal couplingmeans 215 allowing a needle assembly 216 to be releasably mounted,proximal coupling means in the form of two opposed protrusions 211allowing a cap 207 to be releasably mounted covering the cartridgeholder and a mounted needle assembly, as well as a protrusion 212preventing the pen from rolling on e.g. a table top. In the housingdistal end a nut element 225 is fixedly mounted, the nut elementcomprising a central threaded bore 226, and in the housing proximal enda spring base member 208 with a central opening is fixedly mounted. Adrive system comprises a threaded piston rod 220 having two opposedlongitudinal grooves and being received in the nut element threadedbore, a ring-formed piston rod drive element 230 rotationally arrangedin the housing, and a ring-formed clutch element 240 which is inrotational engagement with the drive element (see below), the engagementallowing axial movement of the clutch element. The clutch element isprovided with outer spline elements 241 adapted to engage correspondingsplines 204 (see FIG. 4B) on the housing inner surface, this allowingthe clutch element to be moved between a rotationally locked proximalposition, in which the splines are in engagement, and a rotationallyfree distal position in which the splines are out of engagement. As justmentioned, in both positions the clutch element is rotationally lockedto the drive element. The drive element comprises a central bore withtwo opposed protrusions 231 in engagement with the grooves on the pistonrod whereby rotation of the drive element results in rotation andthereby distal axial movement of the piston rod due to the threadedengagement between the piston rod and the nut element. The drive elementfurther comprises a pair of opposed circumferentially extending flexibleratchet arms 235 adapted to engage corresponding ratchet teeth 205arranged on the housing inner surface. The drive element and the clutchelement comprise cooperating coupling structures rotationally lockingthem together but allowing the clutch element to be moved axially, thisallowing the clutch element to be moved axially to its distal positionin which it is allowed to rotate, thereby transmitting rotationalmovement from the dial system (see below) to the drive system. Theinteraction between the clutch element, the drive element and thehousing will be shown and described in greater detail with reference toFIGS. 4A and 4B.

On the piston rod an end-of-content (EOC) member 228 is threadedlymounted and on the distal end a washer 227 is rotationally mounted. TheEOC member comprises a pair of opposed radial projections 229 forengagement with the reset tube (see below).

The dial system comprises a ratchet tube 250, a reset tube 260, a scaledrum 270 with an outer helically arranged row of dose numerals, auser-operated dial member 280 for setting a dose of drug to be expelled,a release button 290 and a torque spring 255 (see FIG. 3). The resettube is mounted axially locked inside the ratchet tube but is allowed torotate a few degrees (see below). The reset tube comprises on its innersurface two opposed longitudinal grooves 269 adapted to engage theradial projections 229 of the EOC member, whereby the EOC can be rotatedby the reset tube but is allowed to move axially. The clutch element ismounted axially locked on the outer distal end portion of the ratchettube 250, this providing that the ratchet tube can be moved axially inand out of rotational engagement with the housing via the clutchelement. The dial member 280 is mounted axially locked but rotationallyfree on the housing proximal end, the dial ring being under normaloperation rotationally locked to the reset tube (see below), wherebyrotation of dial ring results in a corresponding rotation of the resettube and thereby the ratchet tube. The release button 290 is axiallylocked to the reset tube but is free to rotate. A return spring 295provides a proximally directed force on the button and the theretomounted reset tube. The scale drum 270 is arranged in thecircumferential space between the ratchet tube and the housing, the drumbeing rotationally locked to the ratchet tube via cooperatinglongitudinal splines 251, 271 and being in rotational threadedengagement with the inner surface of the housing via cooperating threadstructures 203, 273, whereby the row of numerals passes the windowopening 203 in the housing when the drum is rotated relative to thehousing by the ratchet tube. The torque spring is arranged in thecircumferential space between the ratchet tube and the reset tube and isat its proximal end secured to the spring base member 208 and at itsdistal end to the ratchet tube, whereby the spring is strained when theratchet tube is rotated relative to the housing by rotation of the dialmember. A ratchet mechanism with a flexible ratchet arm 252 is providedbetween the ratchet tube and the clutch element, the latter beingprovided with an inner circumferential teeth structures 242, each toothproviding a ratchet stop such that the ratchet tube is held in theposition to which it is rotated by a user via the reset tube when a doseis set. In order to allow a set dose to be reduced a ratchet releasemechanism 262 is provided on the reset tube and acting on the ratchettube, this allowing a set dose to be reduced by one or more ratchetincrements by turning the dial member in the opposite direction, therelease mechanism being actuated when the reset tube is rotated theabove-described few degrees relative to the ratchet tube.

Having described the different components of the expelling mechanism andtheir functional relationship, operation of the mechanism will bedescribed next with reference mainly to FIGS. 3A and 3B.

The pen mechanism can be considered as two interacting systems, a dosesystem and a dial system, this as described above. During dose settingthe dial mechanism rotates and the torsion spring is loaded. The dosemechanism is locked to the housing and cannot move. When the push buttonis pushed down, the dose mechanism is released from the housing and dueto the engagement to the dial system, the torsion spring will now rotateback the dial system to the starting point and rotate the dose systemalong with it.

The central part of the dose mechanism is the piston rod 220, the actualdisplacement of the plunger being performed by the piston rod. Duringdose delivery, the piston rod is rotated by the drive element 230 anddue to the threaded interaction with the nut element 225 which is fixedto the housing, the piston rod moves forward in the distal direction.Between the rubber piston and the piston rod, the piston washer 227 isplaced which serves as an axial bearing for the rotating piston rod andevens out the pressure on the rubber piston. As the piston rod has anon-circular cross section where the piston rod drive element engageswith the piston rod, the drive element is locked rotationally to thepiston rod, but free to move along the piston rod axis. Consequently,rotation of the drive element results in a linear forwards movement ofthe piston. The drive element is provided with small ratchet arms 234which prevent the drive element from rotating clockwise (seen from thepush button end). Due to the engagement with the drive element, thepiston rod can thus only move forwards. During dose delivery, the driveelement rotates anti-clockwise and the ratchet arms 235 provide the userwith small clicks due to the engagement with the ratchet teeth 205, e.g.one click per unit of insulin expelled.

Turning to the dial system, the dose is set and reset by turning thedial member 280. When turning the dial, the reset tube 260, the EOCmember 228, the ratchet tube 250 and the scale drum 270 all turn withit. As the ratchet tube is connected to the distal end of the torquespring 255, the spring is loaded. During dose setting, the arm 252 ofthe ratchet performs a dial click for each unit dialled due to theinteraction with the inner teeth structure 242 of the clutch element. Inthe shown embodiment the clutch element is provided with 24 ratchetstops providing 24 clicks (increments) for a full 360 degrees rotationrelative to the housing. The spring is preloaded during assembly whichenables the mechanism to deliver both small and large doses within anacceptable speed interval. As the scale drum is rotationally engagedwith the ratchet tube, but movable in the axial direction and the scaledrum is in threaded engagement with the housing, the scale drum willmove in a helical pattern when the dial system is turned, the numbercorresponding to the set dose being shown in the housing window 202.

The ratchet 252, 242 between the ratchet tube and the clutch element 240prevents the spring from turning back the parts. During resetting, thereset tube moves the ratchet arm 252, thereby releasing the ratchetclick by click, one click corresponding to one unit IU of insulin in thedescribed embodiment. More specifically, when the dial member is turnedclockwise, the reset tube simply rotates the ratchet tube allowing thearm of the ratchet to freely interact with the teeth structures 242 inthe clutch element. When the dial member is turned counter-clockwise,the reset tube interacts directly with the ratchet click arm forcing theclick arm towards the centre of the pen away from the teeth in theclutch, thus allowing the click arm on the ratchet to move “one click”backwards due to torque caused by the loaded spring.

To deliver a set dose, the push button 290 is pushed in the distaldirection by the user as shown in FIG. 3B. The reset tube 260 decouplesfrom the dial member and subsequently the clutch element 240 disengagesthe housing splines 204. Now the dial mechanism returns to “zero”together with the drive element 230, this leading to a dose of drugbeing expelled. It is possible to stop and start a dose at any time byreleasing or pushing the push button at any time during drug delivery. Adose of less than 5 IU normally cannot be paused, since the rubberpiston is compressed very quickly leading to a compression of the rubberpiston and subsequently delivery of insulin when the piston returns tothe original dimensions.

The EOC feature prevents the user from setting a larger dose than leftin the cartridge. The EOC member 228 is rotationally locked to the resettube, which makes the EOC member rotate during dose setting, resettingand dose delivery, during which it can be moved axially back and forthfollowing the thread of the piston rod. When it reaches the proximal endof the piston rod a stop is provided, this preventing all the connectedparts, including the dial member, from being rotated further in the dosesetting direction, i.e. the now set dose corresponds to the remainingdrug content in the cartridge.

The scale drum 270 is provided with a distal stop surface adapted toengage a corresponding stop surface on the housing inner surface, thisproviding a maximum dose stop for the scale drum preventing all theconnected parts, including the dial member, from being rotated furtherin the dose setting direction. In the shown embodiment the maximum doseis set to 80 IU. Correspondingly, the scale drum is provided with aproximal stop surface adapted to engage a corresponding stop surface onthe spring base member, this preventing all the connected parts,including the dial member, from being rotated further in the doseexpelling direction, thereby providing a “zero” stop for the entireexpelling mechanism.

To prevent accidental over-dosage in case something should fail in thedialling mechanism allowing the scale drum to move beyond itszero-position, the EOC member serves to provide a security system. Morespecifically, in an initial state with a full cartridge the EOC memberis positioned in a distal-most axial position in contact with the driveelement. After a given dose has been expelled the EOC member will againbe positioned in contact with the drive element. Correspondingly, theEOC member will lock against the drive element in case the mechanismtries to deliver a dose beyond the zero-position. Due to tolerances andflexibility of the different parts of the mechanism the EOC will travela short distance allowing a small “over dose” of drug to be expelled,e.g. 3-5 IU of insulin.

The expelling mechanism further comprises an end-of-dose (EOD) clickfeature providing a distinct feedback at the end of an expelled doseinforming the user that the full amount of drug has been expelled. Morespecifically, the EOD function is made by the interaction between thespring base and the scale drum. When the scale drum returns to zero, asmall click arm 206 on the spring base is forced backwards by theprogressing scale drum. Just before “zero” the arm is released and thearm hits a countersunk surface on the scale drum.

The shown mechanism is further provided with a torque limiter in orderto protect the mechanism from overload applied by the user via the dialmember. This feature is provided by the interface between the dialmember and the reset tube which as described above are rotationallylocked to each other. More specifically, the dial member is providedwith a circumferential inner teeth structure 281 engaging a number ofcorresponding teeth arranged on a flexible carrier portion 261 of thereset tube. The reset tube teeth are designed to transmit a torque of agiven specified maximum size, e.g. 150-300 Nmm, above which the flexiblecarrier portion and the teeth will bend inwards and make the dial memberturn without rotating the rest of the dial mechanism. Thus, themechanism inside the pen cannot be stressed at a higher load than thetorque limiter transmits through the teeth.

In FIG. 4A the clutch element, the drive element and the housing (inpartial) are shown in the dose setting state, and in FIG. 4B the samecomponents are shown in the expelling state. As appears, the piston rodon which the drive element is arranged and the ratchet tube on which theclutch element is mounted are not shown. To better show the structuresprovided on the inner surface of the housing FIG. 4C shows a partialclutch element 240 arranged in the housing 201.

The inner surface of the housing 201 comprises a circumferentialring-formed array of axially oriented spline elements 204 protrudinginto the interior, each having a pointed distal end 209, as well as acircumferential ring-formed array of one-way ratchet teeth 205. Theinner surface further comprises a male helical thread 203 adapted toengage the female helical thread 273 on the scale drum 270. A distalcircumferential groove is formed to engage and mount the nut element225. The clutch element 240 comprises an inner circumferentialring-formed array of ratchet teeth 242 adapted to engage the ratchet arm252 on the ratchet tube 250, and an outer circumferential ring-formedarray of axially oriented spline elements 241 adapted to engage thespline elements 204 of the housing as well as the coupling slots in thedrive element (see below), each spline having a pointed proximal end243. The drive element 230 comprises a pair of opposed coupling portionseach comprising two proximally extending skirt portions 232 betweenwhich an axially extending coupling slot 233 is formed, the slot beingadapted to engage a portion of the clutch element spline elements. Inthis way the engaging surfaces serve to transmit a rotational force andthereby torque from the clutch element to the drive element in theexpelling state. The drive element further comprises a pair of opposedcircumferentially extending flexible ratchet arms adapted to engage thering-formed array of one-way ratchet teeth 205. During dose delivery,the drive element rotates anti-clockwise and the ratchet arms 235 alsoprovide the user with small clicks due to the engagement with theratchet teeth 205, e.g. one click per unit of insulin expelled. In theshown embodiment 24 ratchet teeth are provided corresponding to 15degrees rotation per unit of insulin. The central bore of the driveelement comprises two opposed protrusions 231 adapted to engage with theaxially oriented grooves on the piston rod.

In the dose setting state shown in FIG. 4A the spline elements 241 ofthe clutch element are in engagement with the spline elements 204 of thehousing thereby rotationally locking the clutch element relative to thehousing. As can be seen from FIG. 4A a group of clutch spline elementsare received in the corresponding coupling slot with a slight rotationalplay. In the expelling state shown in FIG. 4B the spline elements 241 ofthe clutch element are moved distally out of engagement with the splineelements 204 of the housing thereby allowing rotation of the clutchelement relative to the housing. As can be seen from FIG. 4B the groupof clutch spline elements are now received in the corresponding couplingslot without rotational play.

FIG. 5 shows a detail view of the clutch element 240 showing theabove-described inner circumferential ring-formed array of ratchet teeth242 and the outer circumferential ring-formed array of axially orientedspline elements 241. As appears, the spline elements are not arrangedequidistantly on the ring but in groups, the groups comprising twoopposed coupling groups 245 serving as the coupling means engaging thecoupling slots 233. Whereas thus only some of the spline elements serveas coupling means between the clutch element and the drive element theyall serve as coupling means between the clutch element and the housingsplines 204. In the shown embodiment the entire clutch element ismanufactured in magnetic material, preferably moulded using a magneticpolymeric compound containing grinded magnetic particles, as thistechnique can produce intricate shapes. A large magnetic volume issubsequently obtained by magnetizing the whole part, thereby obtaining alarger external magnetic field with a larger magnetic moment than whatwould be possible with just a region of the part being magnetic. In theshown example a magnetic dipole oriented in the A-A direction iscreated. As will be described in greater detail below, the magneticfield can be detected by an electronic sensing component and theinformation be used to determine the rotational and/or axial position ofthe clutch element in relation to the sensor means.

Turning to FIG. 6 an exemplary embodiment of a logging module 300 isshown in which the exterior housing has been removed to reveal theinterior design and components. The module comprises a main body 310having a generally cylindrical ring-formed portion 320 and a bodyportion 330 on which the majority of the electronic circuitry ismounted. The main body is formed from a LDS polymer whereby integratedwiring can be achieved by using LDS (Laser Direct Structuring)technology, the polymer having elastic properties allowing a flexiblehinged latch to be formed integrally. More specifically, the ringportion comprises an inner generally cylindrical surface adapted to bemounted on a drug delivery pen body as well as a pair of opposedintegrally formed coupling structures 321 adapted to engagecorresponding coupling structures on the pen device to assure that themodule is securely mounted. The distal part of the ring portion has alarger diameter with a distally facing circumferential stop surface 329adapted to receive and engage a cap when the module is mounted on a pen,see below.

The inner ring surface and the outer pen body surface may be in eitherform-fitting or slight frictional engagement. Each coupling structure onthe module is in the form of a latch 322 having a proximal portion 323,a distal portion 324 and a central portion, the latter being pivotallyconnected to the ring portion by integrally formed flexible hinges 325allowing the latch to pivot a few degrees corresponding to acircumferential axis. By this arrangement the distal latch portion movesinwards when the proximal portion is moved outwards and vice versa. Theproximal latch portions each comprises an inner protrusion 326 adaptedto engage a corresponding coupling structure on the pen device and thedistal latch portions each comprises a protrusion 327 adapted to engagethe cap when a cap is mounted on the pen body. To assure correctrotational mounting of the module on the pen the shown module isprovided with a funnel-shaped slot 528 (see FIG. 8) adapted to axiallyengage a corresponding protrusion on the pen. In the shown embodiment ofFIG. 1A the protrusion 212 is provided on the pen cartridge holder 210and arranged opposite the pen display window 202, the electronic display130 thereby being arranged next to the pen display window when themodule is mounted on a pen. The interactions between the logging module,the pen body and the cap will be described in greater detail below. Onthe body portion 330 the majority of the electronic components 340including processors means, a display 341, a flexible cap switch 342 anda battery 343 are mounted. In the shown embodiment the logging modulecomprises two opposed sensors in the form of magnetometers 345 mounteddirectly on the ring portion 320, the sensors as well as the majority ofthe electronic components being connected using LDS. Further sensors maybe provided allowing e.g. the type of the device to be recognized. Thelogging module may be provided with user input means in the form of e.g.one or more buttons (not shown) allowing the user to control the module.The logging module may further be provided with transmission meansallowing data to be transmitted to or from the module, e.g. log data maybe transmitted to a user's smartphone by NFC or other wireless means.FIG. 7 shows an alternative embodiment 400 in which the electronicsincluding the sensors are mounted on a flexible PCB 440 which then ismounted on the main body 410 using metal clips 446.

FIG. 8 shows an alternative embodiment of a module main body 510comprising a generally cylindrical ring-formed portion 520 and a bodyportion 530, the main body being formed from a LDS polymer.Corresponding to the FIG. 6 embodiment the ring portion 520 is providedwith a pair of opposed coupling latches 522 having proximal and distalcoupling protrusions 526, 527 as well as a coupling slot 528.

FIG. 9 shows a further alternative embodiment of a module main body 610comprising a generally cylindrical ring-formed portion 620, however, incontrast to the above-described embodiments comprising integrally formedlatches, the latch structures are here provided as separate metal latchmembers 621 attached to the ring portion. Corresponding to theintegrally formed latches, each latch member comprises a proximalportion 623 with an inner protrusion 626 adapted to engage acorresponding coupling structure on the pen device, as well as a distalportion 624 with an inner protrusion 327 adapted to engage the cap whena cap is mounted on the pen body. In the shown embodiment the metallatch members each comprises a pair of proximal legs attached to thering portion by rivets. The shown embodiment of a metal latch does notcomprise a specific hinge structure, however, when mounted on a pen thelatch member will provide the same “dual-purpose” functionality as theintegrally formed latch, see below. FIG. 10 shows the main body 610incorporated in a logging module 600 comprising a circumferential stopsurface 629 and being provided with metal latch members 622.

With reference to FIGS. 2 and 8 mounting and operation of a loggingmodule of the type shown in FIGS. 1A and 1B will be described. To mountthe module on the pen body the cap is removed allowing the module to beslid over the cartridge holder 210. During mounting the user orients themodule display 130 in line with the pen display 202 whereby thefunnel-shaped slot 528 will catch the protrusion 212 which then willorient the module rotationally correct, this ensuring that the proximallatch protrusions 526 will snap into engagement with the cartridgeprotrusions 211, the module now being in its operational position, thisallowing information to be transferred between the drug delivery deviceand the logging module (see below). As appears from FIG. 1B, in themounted position a ring-formed gap 214 is formed between the cartridgeholder and the distal portion of the module, this allowing the cap to beinserted into the gap as shown in FIGS. 1B and 8. For normal use withouta mounted logging module the cap comprises inner coupling means adaptedto engage the cartridge protrusions 211, however, with a mounted loggingmodule the cartridge protrusions are “occupied”. Correspondingly, themodule is provided with the above-described distal latch protrusions 527which in the shown embodiment frictionally engage the outer cap surfaceto securely hold it in place. In addition, also the flexible cap switch342 contributes to hold the cap in place. Alternatively, the cap may beprovided with coupling means, e.g. a circumferential groove, which wouldallow the cap to engage the module by snap action.

The coupling between the pen main part and the module is designed toprovide both ease of attachment and a firm and secure grip during normaluse, however, this should also be the case for the cap when attached tothe pen in cooperation with the module. Correspondingly, when the cap isremoved from the pen a distally directed force is transmitted to thecoupling between the module and the pen via the coupling between themodule and the cap which under given circumstances may result in themodule being unintentionally pulled off the pen. To reduce the risk ofthis happening the module coupling latches 522 are provided with a “snapbooster” feature. More specifically, each latch has a hinged design asdescribed with reference to FIG. 6, this providing that the distal latchportion moves (further) inwards into the circumferential gap when theproximal latch portions are moved outwards as the module is mounted onthe pen. As the proximal latch portions cannot be moved further inwardswhen the module is mounted, the outwards movement of the distal latchportions due to insertion of the cap into the gap 214 will result in aninwardly directed force being applied on the proximal latch portions viathe latch central portion, this ensuring an enhanced grip between themodule and the pen when the cap is mounted, this reducing the risk thatthe module is unintentionally pulled off the pen when the cap isremoved. A proximal stop for the cap is provided by a circumferentialstop surface of the module.

Having described the different components of the system, next a typicalsituation of use will be described with reference to FIGS. 1A and 1B.When the user desires to dispense a dose of drug, e.g. performing anintravenous injection of an amount of an insulin formulation, the cap207 is removed and a needle assembly, if not already in place, ismounted on the cartridge holder coupling means 215. When the cap isremoved the logging module is turned on from its sleeping state byactivation of the module cap switch to its “on” position, e.g. theelectronic circuitry with the sensor system is powered up and thedisplay is turned on showing e.g. the last logged dose and the timesince then. The user will then turn the rotatable dose member 280 tomanually set a desired dose of drug shown in display window 202 andwhich can then be expelled when the button 290 is actuated. Depending onthe design of the logging module a given dose may be registeredcorresponding to a set dose, an expelled dose or both. In the shownembodiment in which movement of the clutch element is detected itfollows that only an expelled dose can be registered. Correspondingly,the module display will not show information in respect of the dosebeing set. When the dose has been set, the user releases thespring-driven expelling mechanism whereby the clutch element is releasedand starts to rotate in a fixed relationship to the expelled amount,this allowing the expelled amount to be determined by the loggingmodule. As the module has not acquired information in respect of the setdose and as the expelling of a set dose can be paused by releasing thepressure on the release button, a given dose, e.g. a large dose, may besplit into two or more amounts, which would result in the logging of twoor more expelled doses. Correspondingly, to treat such split doses as asingle dose the shown logging module is designed to combine and logindividual doses as a single dose under given circumstances, typicallywithin a given window of time, e.g. 5 minutes, after which the “combinefeature” would time out. Such a feature would also allow the module tobe moved to a new pen should a given desired dose be larger than theamount of drug remaining in the cartridge of a used pen. If it for anyreason is desired to have split doses logged individually the “combinewindow” can be closed by mounting the cap on the pen to thereby bringthe cap switch in its “off” position terminating a logging event.Correspondingly, during normal operation in which a given dose isexpelled as a single amount of drug the combine window is closed whenthe cap is mounted, this resulting in the determined dose (single orcombined) being logged in the memory together with a time value as wellas displayed in the electronic display for a given amount of time, e.g.30 seconds, before the electronics power down and the display is turnedoff.

Turning to the sensor system of the logging module, the shown embodimentmay be designed to detect one or more movements of one or more magneticmembers. For example, a “simple” design may be implemented in which thenumber of incremental rotational movements of the clutch element iscounted, i.e. the number of 15 degrees increments, each incrementcorresponding to 1 unit (IU) of insulin. The system would be designed toscan the pen at a frequency sufficiently high to securely detect thatthe clutch element has moved into a new of 24 pre-determined sectorseach corresponding to 15 degrees rotation and thus 1 IU. Using the samebasic sensor design and sensor positions a magnetic drive element couldbe used as an alternative magnetic element. As a further alternativeusing the same general sensor design a component which is moved inaccordance with both the set and the expelled dose could be used as amagnetic element, e.g. the ratchet tube. As the ratchet tube extendsaxially outside the part of the pen enclosed by the module ring only aportion of the ratchet tube may have magnetic properties, e.g. providedby a separate element.

As a yet further alternative the sensor system may be designed todetermine the absolute rotational position of a given element, however,as most pens using a rotating expelling mechanism are designed to expela dose size requiring more than one full rotation of a given element, itwould be necessary to count the number of full revolution. This could beaccomplished using the same magnetic element to both count incrementalmovement (here: number of rotations) and an absolute position. The sameor different sensor systems may be provided to detect the two type ofinformation. Determination of an absolute position would prevent errorsdue to missed counts. Alternatively the sensor system may be designed touse an additional “secondary” element which is moved axially as a doseis expelled to indicate full rotations of the “primary” rotatingelement, e.g. a magnetic EOC member, however, as the movement of such anelement primarily takes place outside the part of the pen enclosed bythe module ring it may be necessary to provide further sensors.

In the following a magnetometer-based detection system will be describedwhich basically can accurately detect the position of a magnet moving ina predefined way, e.g. rotating relative to an axis. The system istherefore applicable in many technical areas in which accuratenon-contact position sensing is relevant. In the following a system willbe described which has been set up for application in a drug deliverysystem comprising a magnetic member which is configured to perform arotational movement, see e.g. FIG. 4A, and which will determine theabsolute rotational position of a magnetic member.

In FIG. 6 an exemplary embodiment of a sensor assembly is configured ascomprising 3 3D magnetic sensors 345 equidistantly around thepre-determined axis for the above-described ring-formed clutch elementrotating inside the distal portion of a pen-formed drug delivery.

In the following an exemplary algorithm for estimating a currentorientation of a magnet will be described. The algorithm is general toany movement of a magnet, but in the present application, it is appliedto a system with rotational movement of a magnet.

The algorithm is adapted for a system having deviations from nominalmovement of the magnet. Therefore, it requires a pre-determined model ofthe magnet movement from which one can derive derivatives. Let B_(nom)^(k)(n) denote the field having nominal geometry of the system, where nis the position of the axial displacement and k is the sensor measuringthe field.

If the magnet has a given geometry and if the relative distance betweensensors and magnet is assumed to be in the magnetic far-field for allpositions, the pre-determined model can be estimated using a dipolefield model. Thus, we can estimate B_(nom) ^(k)(n) to all positions bythe following:

$\begin{matrix}{{B_{nom}^{k}(n)} = {\frac{1}{4\pi}\left\lbrack {\frac{3\left( {m \cdot r} \right)}{r^{5}} - \frac{m}{r^{3}}} \right\rbrack}} & \lbrack 1\rbrack\end{matrix}$

Where m is the dipole moment vector of that given position n, r is thedistance vector between the magnet and the sensor k and r is thedistance between the magnet and sensor k.

If the sensors are positioned in the magnetic near-field, then B_(nom)^(k)(n) can be estimated using Finite Element analysis of the magnetgeometry.

The concept is to have a model that both estimates the non-nominalbehaviour and compensates the pre-determined nominal model, ifnon-nominal behaviour is found to be acceptable. In order to do so, alinearized model of the pre-determined model is defined:

$\begin{matrix}{{{\hat{B}}_{k,n}\left( {B^{ext},{\Delta\; x},{\Delta\; y},{\Delta\; z},{\Delta\; m},{\Delta\;\varphi},{\Delta\;\psi}} \right)} = {{B_{nom}^{k}(n)} + B^{ext} + {\left\lbrack \frac{\partial B}{\partial x} \right\rbrack_{k,n}^{nom}\Delta\; x} + {\left\lbrack \frac{\partial B}{\partial y} \right\rbrack_{k,n}^{nom}\Delta\; y} + \ldots + {\left\lbrack \frac{{\partial B}\;}{\partial\psi} \right\rbrack_{k,n}^{nom}\Delta\;\psi}}} & \lbrack 2\rbrack\end{matrix}$

Where we have included the following Deviation parameters in thelinearized model:

-   -   B^(ext) Uniform background field    -   Δx, Δy Radial offsets of magnet position relative to nominal        model    -   Δz Axial offset of magnet position relative to nominal model    -   Δm Deviation from nominal magnet strength    -   Δφ Rotational offset    -   Δψ Tilt offset

Stacking the Deviation parameters in a column vector E:

$\begin{matrix}{E = \begin{bmatrix}\overset{\_}{B_{x}^{ext}} \\\overset{\_}{B_{y}^{ext}} \\B_{z}^{ext} \\{\Delta\; x} \\{\Delta\; y} \\{\Delta\; z} \\{\Delta\; m} \\{\Delta\;\varphi} \\{\Delta\;\psi}\end{bmatrix}} & \lbrack 3\rbrack\end{matrix}$

We can write a linearized model as:{circumflex over (b)} _(n)(E)=b _(n) ^(nom) +J _(n) E  [4]

Where J_(n)=∂b_(n) ^(nom)/∂E is the Jacobian matrix. Then we determine Eto minimize the difference between the measured field and the linearizedmodel. I.e.:

$\begin{matrix}{\frac{\partial{{b^{meas} - {{\hat{b}}_{n}(E)}}}}{\partial E} = {{2J_{n}^{T}{G_{n}\left( {b_{n}^{nom} + {J_{n}E} - b^{meas}} \right)}} = 0}} & \lbrack 5\rbrack\end{matrix}$

Where G_(n) denotes a diagonal matrix with weights for each sensor k andposition n. Thus, E is given by:E _(n) ^(min) =[J _(n) ^(T) G _(n) J _(n)]⁻¹ [J _(n) ^(T) G _(n)(b^(meas)-b _(n) ^(nom))]  [6]

The above expression can be simplified to the following:E _(n) ^(min) =M _(n)(b ^(meas) −b _(n) ^(nom))  [7]Where:M _(n) =[J _(n) ^(T) G _(n) J _(n)]⁻¹ [J _(n) ^(T) G _(n)]  [8]

This matrix is constant. Thus, it can be stored on the processor to savecomputational power.

The parameter offset vector, E_(n) ^(min), is then inserted into thelinearized model:{circumflex over (b)} _(n)(E _(n) ^(min))=b _(n) ^(nom) +J _(n) E _(n)^(min)  [9]

This provides an updated version of the nominal model accounting for thedifference between the measured field and the nominal model. Theestimated position is found to be the position with the smallestdifference, i.e. minimizing the residual:r _(n) =∥b ^(meas) −{circumflex over (b)} _(n)(E _(n) ^(min))∥  [10]

The advantages of the above algorithm are:

The algorithm makes use of constant tables that can be stored on theprocessor, i.e. it consists of b_(n) ^(nom), J_(n) and M_(n). Thealgorithm provides measures that can be used as fail-safe measure, i.e.the quality of the fit can be estimated from E_(n) ^(min) and the sizeof the residuals, r_(n). The shown column vector E is merely an exampleof selected deviation parameters.

If the risk of external magnetic fields other than earth's magneticfield and disturbances in the internal magnetic field by the presence ofiron nearby can be positively excluded, the most likely candidate ofactual position found in the table can be relayed or displayed as actualposition. However, in most applications the risk of disturbances in themagnetic field must be considered likely from a variety of sources andin some applications the consequences of a wrong determination ofposition could have serious and unacceptable consequences. In suchapplications a number of fail-safe measures can be taken, for example:

-   -   (1) Taking a number of readings and use mean axis value from        each axis from each sensor only when variations between readings        are less than a predefined level. This could prevent wrong        readings from the sensors caused by a fluctuating disturbance in        the magnetic field.    -   (2) Subtracting readings from diametrically opposite sensors to        eliminate the magnet field contribution and the homogenous        external field contribution and hence calculate the gradient of        an inhomogeneous external field. Comparison against threshold        values may be used as criteria for using the readings.    -   (3) Using readings to calculate the external field. Comparison        against threshold values may be used as criteria for using the        readings.    -   (4) Using readings from an over-determined sensor configuration        to calculate deviations from pre-determined nominal mechanical        geometry and magnet characteristics. Comparison against        threshold values may be used as criteria for using the readings.    -   (5) Comparing the deviance of the most likely position and the        deviances of rejected positions (e.g. the second most likely        position) to determine the credibility of the most likely        position. Comparison against threshold values may be used as        criteria for using the readings.    -   (6) Comparing the most likely position and rejected positions,        e.g. the top 10 next most likely positions, to determine the        distribution of the positions. The distribution, e.g. span        between minimum and maximum position, may be used as criteria        for using the readings.    -   (7) Using the most likely position to calculate the field        contribution from the magnet and subtracting the contribution        from the readings to obtain an estimated external field. The        estimated external field may be used as input for calculating a        most likely position which should be rejected by one or more of        the fail-safe measures since the field contribution from the        magnet has been eliminated. The field contribution from a        position different from the most likely positions may be        calculated and added to the estimated external field. The        resulting field may be used as input for calculating a most        likely position. Correspondence between the selected position        and calculated position may be used as criteria for using the        readings.    -   (8) Using calculated positions to determine the mechanical        movement, e.g. direction, speed and position stability.        Comparison against threshold values may be used as criteria for        using the readings.    -   (9) Only appoint a most likely candidate of actual position if        the minimum sum of deviance is less than a predefined value, to        ensure a certain level of coherence between measured values and        (expected) table values. This predefined value may be dependent        on where in the range of operation the most likely candidate is,        since the distances between neighboring candidates vary with        distance from sensor. This should prevent a constant disturbance        above a certain magnitude from causing the wrong position to be        appointed most likely candidate and can also prevent a most        likely candidate from being appointed if one of the sensors        axis' have gone into saturated mode. If sensors are exposed to a        magnetic field of a strength exceeding their limit of operation,        they will go into saturation mode and give a readout of (a known        predefined) maximum value.

The above mentioned fail-safe measures will only be able to help preventread-out of dose data based on false positions by giving no read-out atall. The system can then (if change of position is either prevented ormonitored not to occur) repeat measurements until the system is clear ofthe external disturbance of the internal magnetic field.

As a given pre-filled drug delivery device may be part of a system itmay be provided to the users with different types of drugs, e.g. drugsfor the treatment of different conditions such as diabetes and growthdisorders, different classes of drugs for the treatment of a givencondition such as insulins and GLP-1 for treatment of diabetes,different types of drugs from a given class such as long-acting andfast-acting insulin formulations, or different concentrations for agiven specific drug such as 100 IU or 200 IU of insulin per ml offormulation. Although the above-described logging module normally wouldbe designed to be mounted on only one type of drug delivery device itcould in theory be mounted on devises containing a variety of differentdrugs.

To prevent that a given logging module would be used in a way resultingin incorrect determination of dose data, it should be ensured that agiven logging module in a given state is used in combination with thecorresponding drug.

For example, a given logging module may be adapted to be used with onlyone type of drug, e.g. a given insulin formulation having a givenconcentration, this being indicated on the logging module e.g. text,colour or other visual markings. Indeed, this would still allow a givenlogging module to be used in combination with the wrong delivery device.To prevent this from taking place the logging module and the differentdelivery devices of a given system may be coded allowing mating of onlymodules and devices corresponding to each other, e.g. mechanically orelectronically.

For example, when a given pen type is used for different types of drugsit will be marked accordingly, e.g. by text, colour and/or codes. Byproviding such visual markings on the pen body on the part of thesurface which would be covered by a mounted logging module, the loggingmodule could be provided with optical sensor means adapted to detectsuch markings. For example, a given pen device may be fully or partlymanufactured from a material having a given colour or it may be providedwith a label having a given colour.

If a given logging module is adapted to be used only for one type ofdrug it would require that the corresponding colour is positivelyidentified, otherwise the logging module would indicate an errorcondition. Alternatively, the logging module may be adapted to be usedin combination with a variety of drugs, such that the positiveidentification of a given pre-specified colour would set up the loggingmodule accordingly. For example, when mounted on a pen device withinsulin of a given concentration it would register and display thecorrect number of IU, whereas when mounted on a pen device with GLP-1 ofa given concentration it would register and display the correct numberof mg. The type or brand name of the drug may be displayed e.g. a shorttime each time the display is turned on.

In the above description of exemplary embodiments, the differentstructures and means providing the described functionality for thedifferent components have been described to a degree to which theconcept of the present invention will be apparent to the skilled reader.The detailed construction and specification for the different componentsare considered the object of a normal design procedure performed by theskilled person along the lines set out in the present specification.

The invention claimed is:
 1. A drug delivery assembly, comprising: adrug delivery device comprising: a drug reservoir or structure forreceiving a drug reservoir, the reservoir comprising an outlet portion,a drug expelling assembly, a logging module releasably attachable to thedrug delivery device and comprising electronic circuitry adapted tocreate a log of expelled dose amounts of drug, comprising: sensorstructure adapted to capture a property value related to a dose amountof drug expelled from a reservoir by the expelling assembly during anexpelling event, processor structure adapted to determine dose amountsbased on captured property values, a cap releasably attachable to thelogging module to cover an outlet portion of a mounted drug reservoir,wherein: the logging module and the drug delivery device comprise matingsnap coupling structure allowing the logging module and the drugdelivery device to be releasably coupled to each other by relativemovement there between in a first direction, the logging modulecomprises locking structure acting on the locking module snap couplingstructure and being actuatable between a locked and an unlocked state,the locking structure is actuated from the unlocked to the locked statewhen the cap, with the logging module coupled to the drug deliverydevice, is attached to the logging module in the first direction, andthe locking structure is actuated from the locked to the unlocked statewhen the cap is detached from the logging module in a second directionopposed to the first direction.
 2. An assembly as in claim 1, whereinthe locking structure in the locked state prevents the logging modulefrom being de-coupled from the drug delivery device.
 3. An assembly asin claim 1, wherein the locking structure in the locked state providesthat an increased force has to be applied in order to de-couple thelogging module from the drug delivery device.
 4. An assembly as in claim1, wherein the logging module snap coupling structure comprises aflexible portion being strained in the attached state, the lockingstructure in the locked state increasing the strain.
 5. An assembly asin claim 1, wherein the cap when attached to the logging module engagesonly the logging module.
 6. An assembly as in claim 1, wherein the capwhen attached to the logging module engages both the logging module andthe drug delivery device.
 7. An assembly as in claim 1, wherein the cap,when the logging module is not attached to the drug delivery device, isreleasably attachable to the drug delivery device.
 8. An assembly as inclaim 1, wherein: the structure for receiving a drug reservoir is acartridge holder adapted to receive a drug reservoir in the form of adrug-filled cartridge, the cartridge comprising an outlet and acylindrical main body portion with an axially displaceable piston, theoutlet being adapted to be arranged in fluid communication with a needleassembly comprising a hollow needle, and the drug expelling assemblycomprises dose setting structure for setting a dose to be expelled, anda drive member adapted to engage and axially move the piston of areceived cartridge to thereby expel an amount of drug from the cartridgethrough the outlet.
 9. An assembly as in claim 8, wherein the expellingassembly comprises a spring which is strained during dose setting andwhich can be released to move the drive member.